Guiding device for metal bellows

ABSTRACT

A guiding device for metal bellows ( 19 ) which comprises a terminal element ( 35 ) on at least one bellows end ( 31 ), said terminal element being movable along the wall of a housing ( 1 ) during expansion and compression of the bellows ( 19 ), a guiding means ( 47 ) being interposed between the terminal element and the housing ( 1 ). The guiding device is characterized in that the guiding means comprises at least one annular element ( 47 ) which surrounds a peripheral zone of the terminal element ( 35 ), said annular element, on its outer periphery, forming first annular sections which are radially spaced apart from the wall of the housing ( 1 ) and which are separated from each other by second annular sections that radially project over the first annular sections.

The invention relates to a guiding device for a metal bellows, whichcomprises an end body on at least one end of the bellows, said end bodybeing movable along the wall of a housing during expansion andcompression of the bellows, between this end body and the housing therebeing a guiding means.

Metal bellows are used in various technical fields as a component ofvariable length, for example, when it is necessary to equalize thelength in lines or coupling connections for flowable media. Inparticular, metal bellows are also often used in hydraulic accumulatorsas a movable separating element between the gas side and the fluid side.Especially in applications where relatively extensive movements takeplace during expansion and compression of the bellows, or if back andforth movements take place at a relatively high rate and/or at higheracceleration values, as is the case in pulsation dampers or shockabsorbers, it is important for the service life of the bellows that therespective end of the bellows that is moved along a housing wall inoperation be guided in a safe and reliable manner.

In this respect, the prior art provides a guiding means on the movableend of the bellows involved. In a prior art solution published at alater date, disclosed in German patent application DE 10 2007 036 487.5,the guide arrangement is designed in such a way that individual guidebodies that are distributed around the periphery of the end body arefastened to the peripheral edge of the movable end body of the bellows;and these guide bodies form sliding bodies that are guided so as to restwith an outer sliding surface against the wall of the housing. Thesliding surfaces of these bodies are spaced radially apart from theperipheral edge of the end body, so that fluid passages are formed alongthe housing wall between the individual guide bodies.

These guide bodies are designed as guide shoes; and, when the end bodyis configured in the form of a cup, the guide shoes overlap theperipheral edge of the cup, which has a circular cylindrical side wallthat extends into the interior of the bellows. When the guide bodies aremade of a plastic material with good sliding properties, good guideproperties are attained; that is, when the friction ratio between theguide body and the housing wall is favorable, the guide provides safeand reliable long term operation. On the other hand, the production iscomplex and cost intensive. The individual guide bodies, which arefabricated in a separate production step, have to be brought to theassembly site and mounted on the end edge of the end body of thepertinent bellows. In order to ensure a reliable anchoring of the guidebodies, the guide bodies are designed as guide shoes, having a profilethat is similar to the shape of a U in the cross section, with legs thatoverlap the end edge of the cup-like end body. In this context, the endedge of the cup has to have a catch, and the interior of the profile ofthe guide shoes has to have at least one undercut in order to make itpossible to secure the guide bodies with a snap lock action. Theformation of the undercuts involves a time-consuming and costlyproduction of the guide shoes by compression molding.

In light of the above-described prior art, the object of the presentinvention is to provide a guiding device that is distinguished by asignificant simplification of the production process and, as a result, areduction in the production costs while at the same time retaining thegood guide and operating properties of the aforementioned solution knownfrom the prior art.

This object is achieved according to the present invention by a guidingdevice having the features specified in claim 1 in its entirety.

Accordingly, an important particularity of the invention resides in thefact that the guiding means comprises an annular element, whichsurrounds a peripheral region of the end body of the bellows, and thatthe annular element forms both annular sections, which are radiallyspaced apart from the wall of the housing, on the outer periphery ofthis annular element and also forms second annular sections, which aredistributed over the outer periphery and project radially beyond thefirst annular sections. At the same time, these radially projectingannular sections form the sliding surfaces that are provided on the wallof the housing and separate the first annular sections, which areradially recessed relative to said sliding surfaces, from each other inthe circumferential direction. Therefore, a uniform annular elementassumes not only the function of the guide bodies known from thesolution according to the prior art, but also takes over the formationof the fluid passages between the housing wall and the end body of thebellows at the first annular sections, which are situated between thesecond annular sections and which are radially recessed.

Preferably, the annular element is made of a plastic material with goodsliding properties, so that the result is a lightweight design that iseasy to manufacture by injection molding.

In preferred embodiments, the bellows is secured at the bellows end,which lies opposite the movable end body, at a retaining ring that isrigidly mounted on the housing and that seals off the interior of thebellows relative to the wall of the housing, so that the end body formsa closure body that tightly closes off the interior of the bellows atthe assigned end of the bellows. Such a design is especiallyadvantageous when the metal bellows is used as a movable separatingelement between the gas side and the fluid side of a hydraulicaccumulator.

The arrangement can be configured in such an advantageous way that therespective annular element has a ring portion that forms the firstannular sections and that engages with a circumferential annular groove,which is arranged on the end body. This enlargement of the distance fromthe guide location to the immovable end of the bellows supports the tiltresistance of the guide. Securing the annular element by snapping intoan annular groove renders the assembly process especially simple andeasy.

In especially advantageous embodiments, the annular element can exhibitan internal ring portion with at least one inner edge, which projectsradially inward into the assigned annular groove, and an external ringportion having an exterior, on which are formed the first and the secondannular sections, with the external ring portion and the first and thesecond annular sections having a larger axial width than the width ofthe annular groove and the width of the accommodated inner edge of theinternal ring portion. Such a design of the annular element offers thepossibility of forming the axial dimensions of the second annularsections, which are formed on the external ring portion and which formthe actual sliding surfaces on the housing wall, with dimensions thatare axially much larger than those corresponding to the width of theannular groove securing the annular element. As a result, the slidingsurfaces that are expanded accordingly in the axial direction exhibitoptimal guide properties at the wall of the housing.

The arrangement can be configured in such an advantageous way that theend of the internal ring portion of the annular element that liesclosest to the bottom of the housing forms a radially inward projectinglip, which extends inward from the radially external edge region andlimits the edge region to a narrow annular surface. Hence, when thedevice is running, a narrow, axially projecting edge region forms acontact face when making contact with the surface of the housing bottomduring the fully expanded state of the bellows. When the annular elementimpinges on the bottom surface, the resilience of the plastic material,of which the annular element is made, acts as a damping element, so thatthe risk of adhering to the housing bottom is eliminated due to the factthat the size is reduced on account of the inclined surface of theformed contact face.

Preferably, the second annular sections are arranged at equal angulardistances from each other respectively. However, for a low friction, butsafe and reliable guide, there are preferably 4 to 12 second annularsections on the pertinent annular element.

The subject matter of the invention according to claim 8 is also ahydraulic accumulator with an accumulator housing, which has a metalbellows as the movable separating element between a gas side and a fluidside; and there is a guiding device according to one of claims 1 to 7for said metal bellows.

The invention is explained in detail below by means of one embodimentshown in the drawings. Referring to the drawings,

FIG. 1 is a longitudinal sectional view of a hydraulic accumulator,which is depicted in a highly simplified schematic form and slightlyreduced in size compared to a practical embodiment, with said hydraulicaccumulator being provided for use as a shock absorber and having ametal bellows, which serves as the movable separating element betweenthe gas side and the fluid side and is provided with a guiding deviceaccording to one exemplary embodiment of the invention;

FIG. 2 is a top view of the hydraulic accumulator (shown in FIG. 1) thatis partially cut open;

FIG. 3 is a perspective oblique view of just the annular element as anessential component of the guiding device of the exemplary embodiment;

FIG. 4 is a top view of the annular element from FIG. 3.

FIG. 5 is a sectional view along the intersecting line from FIG. 4; and

FIG. 6 shows a detail of just the area designated as XIII in FIG. 5 anddrawn on a larger scale than in FIG. 5.

FIGS. 1 to 6 show an exemplary embodiment of the inventive guidingdevice in a hydraulic accumulator in the form of a shock absorber. Anaccumulator housing, designated as a whole as 1, comprises a mainhousing part 3 in the form of a circular cylindrical cup, which isclosed on the end situated at the top in the drawing, with the exceptionof a fill port 7, which is in alignment with the longitudinal axis 9 ofthe housing and is closed off in a fluid-tight manner by means of a weldnugget in the drawing from FIG. 1. In order to close the upper end ofthe cup, a closure part 13 is tightly welded to the main housing part 3along a welding line 16. A fluid inlet 15 with an outer connecting pipe17 is arranged concentrically to the axis 9 in the bottom 69 of the cup.In the drawing from FIG. 1, a thread protection cap 20 is screwed ontothe outer thread of the connecting pipe 17.

In the interior of the accumulator housing, a metal bellows unit forms amovable separating element between a gas side 21, which borders on theclosure part 13 and can be filled via the fill port 7 with a workinggas, preferably N₂, at a gas prefill pressure. In the drawing from FIG.1, the bellows 19 is in its fully expanded state, with the volume of thegas side 21 having the maximum value, whereas the fluid side 23,adjacent to the fluid inlet 15, exhibits its minimum value. The bellowsunit is welded in a fluid-tight manner to a metal retaining ring 25 withthe bellows end 29 adjacent to the closure part 13 of the housing—statedmore precisely, on the radially external edge of the last bellows fold.The retaining ring 25 in turn is welded to the accumulator housing atthe point of separation between the closure part 13 and the main part 3at the welding line 16. When the accumulator housing is assembled andintegrated into the bellows unit, the welding line 16 therefore isheat-insulated at least to some extent from the bellows end 29 by theretaining ring 25. The weld area of the bellows end 29 at the retainingring 25 is at the site designated as 27 in the figure, where theretaining ring 25 forms an axial bulge as the weld area.

The movable bellows end 31, lying opposite the bellows end 29 that isrigidly mounted in the housing, is welded to a metal end body 35 at theradially external end edge of the last bellows fold. This end body formsa closure body that closes in a fluid-tight manner the interior of thebellows 19 and, as a result, forms the separation between the gas side21 and the fluid side 23.

A cylindrical insert body 73, which extends from the closure part 13into the interior of the bellows 19, has the effect of suitably reducingthe volume of the gas side 21 and forms at the same time an end stopabutment, against which the movable end body 35 of the bellows 19 in itsfully compressed state strikes. FIG. 1 shows the bellows 19 in itsalmost fully expanded position, in which the end body 35 is at a shortdistance from the flat bottom area 71 of the bottom 69.

The end body 35 has a more or less flat surface on the side facing theinterior of the bellows 19, apart from a peripheral edge 75, whichprojects slightly in the axial direction and forms the welding spot atthe assigned bellows end 31. Axially offset from the peripheral edge 75,the end body 35 forms an annular groove 77 as the seat for an internalring portion 79 of the annular element 47 of the guiding device. Axiallyoffset relative to the annular groove 77, the end body 35 forms a stepwith a step surface against which rests a radially inward projecting lip81 of the ring portion 79. The annular element 47, depicted in FIGS. 3to 6, has an external ring portion 83, which is connected in a radiallyoutward manner to the internal ring portion 79. This external ringportion forms the inner annular sections 51, which are separated fromeach other by outer annular sections 53, which form externally on theradially projecting guide bodies 55 the sliding surfaces for contactwith the housing wall. The annular element 47 is made of a plasticmaterial with good sliding properties and can be fabricated by turningor milling, but can also be formed as a compression molded component.

One particularity of the annular element 47 resides, as best seen inFIG. 6, in the fact that the lip 81 forms on inclined surface 87 betweenthe radially outer end 85 and its inner end, so that the annular element47 forms a relatively narrow edge region at the end 85. Therefore, whenthe annular element 47 is attached to the end body 35 of the bellows,this axially projecting edge region forms the contact face at the end 85when making contact with the bottom area 71 of the bottom 69 during thefully expanded state of the bellows 19. The resilience of the plasticmaterial, of which the annular element 47 is made, acts as a dampingelement when impinging on the bottom area 71 so that the risk ofadhering to the bottom area 71 is eliminated due to the fact that thesize is reduced on account of the inclined surface 87 of the formedelevation area. Not only can the guide provide support, but also thebellows body, in particular in its end regions, can provide support. Asa result, the overall axial length of the guide could then be shorter.

In the event that the diameter of the bellows 19 is large, a pluralityof annular sections 53 would be necessary to provide support than wouldbe the case for bellows having smaller diameters. In the event of a verysmall diameter, three annular sections 53, which are arranged so as tobe offset by 120° from each other respectively, are provided at theannular element 47.

An additional particularity resides in the fact that the guide bodies 55and, thus, the sliding surfaces formed by the outer annular sections 53exhibit a much larger axial length than would be the case with anannular element 47 forming a flat ring.

When the hydraulic accumulator that is provided with the guiding deviceaccording to the invention is used as a pulsation damper, the fluid side23 is in fluid connection with a pressure fluid, in particular ahydraulic fluid, a fuel, or lubricant, by way of the inlet 15, in orderto stabilize any pressure surges. In this context, it has proven to bepractical if, as disclosed in DE 10 2004 004 341 A1, the gas side 21 isfilled not only with a working gas, but also with a specifiable volumefraction of a fluid. In this case, it has proved to be especiallyadvantageous for the gas side 21 of the accumulator to have as thefilling a combination of nitrogen gas as the working gas and ethylenealcohol as the fluid. In operation, the fluid can form a damping supportmedium between the folds and the deflections of the bellows 19; and thisdamping support medium can provide support as an abutment for the foldedwall portions of the bellows 19 at the fluid, a feature that extends theservice life of the bellows and, thus, enhances the operationalreliability. The same applies, in particular, to rapid pulsations andfast pressure surges.

1. A guiding device for a metal bellows (19), which comprises an endbody (35) on at least one bellows end (31), said end body being movablealong the wall of a housing (1) during expansion and compression of thebellows (19), between this end body and the housing (1) there being aguiding means (47), characterized in that the guiding means comprises atleast one annular element (47), which surrounds a peripheral region ofthe end body (35); and that the outer periphery of this annular elementforms first annular sections (51), which are radially spaced apart fromthe wall of the housing (1) and are separated from each other by secondannular sections (53), which are distributed over the outer peripheryand project radially beyond the first annular sections (51).
 2. Theguiding device according to claim 1, characterized in that the annularelement (47) is made of a plastic material with good sliding properties.3. The guiding device according to claim 1, characterized in that thebellows (19) is secured at the bellows end (29), which lies opposite themovable end body (35), at a retaining ring (25) that is rigidly mountedin the housing; and this retaining ring seals off the interior of thebellows (19) relative to the wall of the housing (1), and that the endbody (35) forms a closure body that tightly closes off the interior ofthe bellows (19) at the assigned bellows end (31).
 4. The guiding deviceaccording to claim 1, characterized in that the respective annularelement (47) has a ring portion (49) that forms the first annularsections (51) and that engages with a circumferential annular groove(77), which is arranged on the end body (35).
 5. The guiding deviceaccording to claim 1, characterized in that the respective annularelement (47) has an internal ring portion (79) with at least one inneredge, which projects radially inward into the assigned annular groove(77), and an external ring portion (83) having an exterior, on which areformed the first and the second annular sections (51, 53), and that theexternal ring portion (83) and the first and the second annular sections(51, 53) have a larger axial width than the width of the annular groove(77) and the width of the accommodated inner edge of the internal ringportion (79).
 6. The guiding device according to claim 5, characterizedin that the end of the internal ring portion (79) that lies closest tothe bottom (69) of the housing (1) forms a radially inward projectinglip (81), which extends inward from the radially external edge region(85) and limits the edge region (85) to a narrow annular surface.
 7. Theguiding device according to claim 1, characterized in that the secondannular sections (53) are arranged at equal angular distances from eachother respectively; and that there are preferably three to twelve secondannular sections (53) at the annular element (47).
 8. A hydraulicaccumulator comprising an accumulator housing (1), which is providedwith a metal bellows (19) as the movable separating element between agas side (21) and a fluid side (23); and there is a guiding device (47)according to claim 1, for said metal bellows.